Polishing apparatus and polishing method for polishing a periphery of a substrate

ABSTRACT

A polishing apparatus capable of accurately detecting a polishing end point of a periphery of a substrate, such as a wafer, is disclosed. The polishing apparatus includes a polishing head configured to press a polishing tool against the periphery of the substrate on a substrate holding surface. The polishing head includes a pressing member configured to press the polishing tool against the periphery of the substrate, and a shear-force detection sensor configured to detect a shear force acting on the pressing member and output an index value indicating a magnitude of the shear force. An operation controller has a memory storing a program configured to determine a polishing end point at which the index value reaches a threshold value, and a processer configured to execute the program.

CROSS REFERENCE TO RELATED APPLICATION

This document claims priority to Japanese Patent Application Number2018-135649 filed Jul. 19, 2018, the entire contents of which are herebyincorporated by reference.

BACKGROUND

In a manufacturing process of a semiconductor device, various kinds offilms are formed on a periphery of a wafer. Since these films may causeparticles, the films need to be removed from the periphery. Therefore, apolishing apparatus, which includes a polishing tool such as a polishingtape, is used to polish the periphery of the wafer to remove the filmfrom the periphery. The polishing apparatus is configured to press thepolishing tool against the periphery of the wafer, while rotating thewafer about its axis, to thereby polish the periphery.

Polishing of the periphery of the wafer is terminated when the film isremoved from the periphery. However, it is practically difficult toaccurately detect a point of time at which the film is removed from theperiphery. Thus, in a conventional technique, polishing of a peripheryof a wafer is terminated when a preset time has elapsed. If a filmresidue exists on the polished periphery, an additional polishing isperformed.

However, the time required for removing the film from the periphery ofthe wafer can vary depending on conditions of the film and the polishingtool, a portion of the wafer to be polished, and other factors.Therefore, the film may still exist on the wafer when the preset timehas elapsed. If a polishing time is increased so as to prevent suchinsufficient polishing, a cost of consumables used for polishing onewafer is increased. Moreover, such an increase in the polishing time mayresult in excessive polishing of the periphery of the wafer.

SUMMARY OF THE INVENTION

According to embodiments, there are provided a polishing apparatus and apolishing method capable of accurately detecting a polishing end pointof a periphery of a substrate, such as a wafer.

Embodiments, which will be described below, relate to an apparatus and amethod for polishing a periphery of a substrate, such as a wafer, andmore particularly to a technique for detecting a polishing end point ofthe periphery of the substrate.

In an embodiment, there is provided a polishing apparatus for polishinga periphery of a substrate, comprising: a substrate holder having asubstrate holding surface for holding the substrate, the substrateholder being configured to rotate the substrate holding surface; apolishing head configured to press a polishing tool against theperiphery of the substrate on the substrate holding surface; and anoperation controller configured to control operations of the substrateholder and the polishing head, wherein the polishing head comprises: apressing member configured to press the polishing tool against theperiphery of the substrate; and a shear-force detection sensorconfigured to detect a shear force acting on the pressing member due toa frictional resistance between the polishing tool and the periphery ofthe substrate, the shear-force detection sensor being configured tooutput an index value indicating a magnitude of the shear force, andwherein the operation controller comprises a memory storing a programconfigured to determine a polishing end point at which the index valuereaches a threshold value, and a processer configured to execute theprogram.

In an embodiment, the shear-force detection sensor comprises a tactilesensor including a sensor element having carbon microcoils, and thesensor element is fixed to the pressing member.

In an embodiment, the sensor element further has an elastic resin block,and the carbon microcoils are located in the elastic resin block.

In an embodiment, the polishing head has a polishing-tool pressingsurface configured to support a back side of the polishing tool and topress the polishing tool against the periphery of the substrate. and atleast a part of the polishing-tool pressing surface is constituted bythe sensor element.

In an embodiment, the shear-force detection sensor comprises a load cellcoupled to a back side of the pressing member.

In an embodiment, there is provided a polishing method of polishing aperiphery of a substrate, comprising: holding the substrate on asubstrate holding surface; rotating the substrate holding surfacetogether with the substrate; polishing the periphery of the substrate bypressing a polishing tool with a pressing member of a polishing headagainst the periphery of the substrate; during polishing of theperiphery of the substrate, detecting a shear force acting on thepressing member due to a frictional resistance between the polishingtool and the periphery of the substrate by a shear-force detectionsensor; determining a polishing end point at which an index valueindicating a magnitude of the shear force reaches a threshold value; andterminating polishing of the periphery of the substrate based on thepolishing end point.

In an embodiment, the shear-force detection sensor comprises a tactilesensor including a sensor element having carbon microcoils, and thesensor element is fixed to the pressing member.

In an embodiment, the sensor element further has an elastic resin block,and the carbon microcoils are located in the elastic resin block.

In an embodiment, the polishing head has a polishing-tool pressingsurface configured to support a back side of the polishing tool and topress the polishing tool against the periphery of the substrate, and atleast a part of the polishing-tool pressing surface is constituted bythe sensor element.

In an embodiment, the shear-force detection sensor comprises a load cellcoupled to a back side of the pressing member.

When a film on the periphery of the substrate is removed by thepolishing tool, an underlying layer is exposed. A frictional resistancebetween the film and the polishing tool is different from a frictionalresistance between the underlying layer and the polishing tool. Thefrictional resistance acts as a shear force on the pressing member. Whenthe underlying layer is exposed as a result of polishing of thesubstrate, the shear force changes. Therefore, the polishing end pointcan be accurately detected based on the change in the shear force.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B are enlarged cross-sectional views each showing aperiphery of a substrate;

FIG. 2 is a schematic view showing a polishing apparatus for polishing aperiphery of a wafer which is an example of a substrate;

FIG. 3 is a top view of the polishing apparatus shown in FIG. 2;

FIG. 4 is a view showing a polishing head which tilts up and down;

FIG. 5 is an enlarged view of the polishing head shown in FIG. 2;

FIG. 6 is a perspective view showing a shear-force detection sensorshown in

FIG. 5;

FIG. 7 is a perspective view showing another embodiment of theshear-force detection sensor;

FIG. 8 is a graph showing an index value of a shear force thatfluctuates periodically;

FIG. 9 is a schematic view showing a configuration of an operationcontroller; and

FIG. 10 is a schematic view showing a computing system that can be usedfor setting an optimal polishing recipe.

DESCRIPTION OF EMBODIMENTS

Embodiments will now be described with reference to the drawings.

FIG. 1A and FIG. 1B are enlarged cross-sectional views each showing aperiphery of a substrate. More specifically, FIG. 1A shows across-sectional view of a so-called straight-type substrate, and FIG. 1Bshows a cross-sectional view of a so-called round-type substrate.Examples of the substrate include a wafer. The periphery of thesubstrate is defined as a region including a bevel portion, a top edgeportion, and a bottom edge portion. In a wafer W shown in FIG. 1A, thebevel portion is an outermost circumferential surface of the wafer W(indicated by a symbol S) that is constituted by an upper slope (anupper bevel portion) P, a lower slope (a lower bevel portion) Q, and aside portion (an apex) R. In a wafer W shown in FIG. 1B, the bevelportion is a portion (indicated by a symbol S) having a curved crosssection and forming an outermost circumferential surface of the wafer W.The top edge portion is an annular flat portion T1 located radiallyinwardly of the bevel portion S. The bottom edge portion is an annularflat portion T2 located opposite the top edge portion and locatedradially inwardly of the bevel portion S. The top edge portion T1 andthe bottom edge portion T2 are connected to the bevel portion S. The topedge portion T1 may include a region where devices are formed.

FIG. 2 is a schematic view showing a polishing apparatus for polishing aperiphery of a wafer which is an example of a substrate. The polishingapparatus includes a substrate holder 32 for holding and rotating awafer W which is an example of a substrate, and a polishing head 34 forpressing a polishing tape 42, serving as a polishing tool, against aperiphery of the wafer W held by the substrate holder 32. The substrateholder 32 includes a substrate holding surface 37 for holding the waferW by a vacuum suction, a stage motor 39 for rotating the substrateholding surface 37, and an XY moving device 38 for translating thesubstrate holding surface 37 and the stage motor 39. The XY movingdevice 38 includes a combination of a ball screw mechanism and aservomotor (not shown) for moving the substrate holding surface 37 andthe stage motor 39 in an X direction, and further includes a combinationof a ball screw mechanism and a servomotor (not shown) for moving thesubstrate holding surface 37 and the stage motor 39 in a Y directionperpendicular to the X direction. The X direction and the Y directionare parallel to the substrate holding surface 37.

The wafer W, with its back surface facing downward, is placed on thesubstrate holding surface 37 by a transporting device (not shown). Agroove 37 a is formed in the substrate holding surface 37. The groove 37a communicates with a vacuum line 40. The vacuum line 40 is coupled to anon-illustrated vacuum source (e.g., vacuum pump). When a vacuum iscreated in the groove 37 a of the substrate holding surface 37 throughthe vacuum line 40, the wafer W is held on the substrate holding surface37 by the vacuum suction. In this state, the stage motor 39 rotates thesubstrate holding surface 37 to rotate the wafer W about its axis. Adiameter of the substrate holding surface 37 is smaller than a diameterof the wafer W. A central region of the back surface of the wafer W isheld by the substrate holding surface 37. The entire periphery of thewafer W protrudes outward from the substrate holding surface 37.

The polishing head 34 is disposed adjacent to the substrate holdingsurface 37. More specifically, the polishing head 34 is disposed so asto face the periphery of the wafer W held on the substrate holdingsurface 37. The polishing head 34 includes a plurality of guide rollers43 for supporting the polishing tape 42 as a polishing tool, a pressingmember (e.g., pressing pad) 44 for pressing the polishing tape 42against the periphery of the wafer W, and an air cylinder 45 as anactuator for providing a pressing force to the pressing member 44.

The air cylinder 45 is coupled to the pressing member 44 and isconfigured to move the pressing member 44 toward the substrate holdingsurface 37. The air cylinder 45 exerts the pressing force on thepressing member 44, which in turn presses the polishing tape 42 againstthe periphery of the wafer W. Instead of the polishing tape, a whetstonemay be used as the polishing tool.

The polishing head 34 is provided with a tape-advancing mechanism 50 foradvancing the polishing tape 42. One end of the polishing tape 42 isconnected to a feeding reel 51, and the other end is connected to atake-up reel 52. The tape-advancing mechanism 50 is configured toadvance the polishing tape 42 at a predetermined speed from the feedingreel 51 to the take-up reel 52 via the polishing head 34. Examples ofthe polishing tape 42 to be used include a tape having abrasive grainsfixed to a surface thereof, and a tape constituted by a hard nonwovenfabric.

Pure-water supply nozzles 57, 58 for supplying pure water onto the waferW are arranged above and below the wafer W held on the substrate holdingsurface 37. The pure-water supply nozzle 57 is located above a center ofthe substrate holding surface 37. The pure water supplied onto an uppersurface of the rotating wafer W spreads over the entire upper surface ofthe wafer W by a centrifugal force, thus covering the entire uppersurface of the wafer W. Therefore, the pure water can prevent particlesfrom adhering to the upper surface of the wafer W during polishing ofthe periphery of the wafer W. The pure-water supply nozzle 58 suppliesthe pure water onto a lower surface of the wafer W and forms a flow ofthe pure water in the radially outward direction. Flow-rate controlvalves 60, 61 are coupled to the pure-water supply nozzles 57, 58,respectively. These flow-rate control valves 60, 61 are configured tocontrol flow rates of the pure water that flows through the pure-watersupply nozzles 57, 58.

FIG. 3 is a top view of the polishing apparatus shown in FIG. 2. Thepolishing head 34 is held by a crank arm 55. More specifically, one endof the crank atm 55 is fixed to the polishing head 34, and the other endof the crank arm 55 is coupled to a servomotor 56. The crank arm 55 as awhole is parallel to the substrate holding surface 37. When theservomotor 56 rotates the crank arm 55 in a clockwise direction and acounterclockwise direction alternately by a predetermined angle, theentire polishing head 34 tilts upward and downward as shown in FIG. 4.

The periphery of the wafer W is polished as follows. The wafer W, heldon the substrate holding surface 37, is rotated about the axis of thewafer W by the stage motor 39. The pure water is supplied from thepure-water supply nozzle 57 onto the upper surface of the rotating waferW, and the pure water is supplied from the pure-water supply nozzle 58onto the lower surface of the rotating wafer W. As shown in FIG. 4, thepolishing head 34 tilts upward and downward while pressing the polishingtape 42 against the periphery of the wafer W. The polishing tape 42 isheld in sliding contact with the periphery of the rotating wafer W inthe presence of the pure water to thereby polish the periphery of thewafer W.

FIG. 5 is an enlarged view of the polishing head 34 shown in FIG. 2. Asshown in FIG. 5, the polishing head 34 includes the pressing member 44for pressing a polishing surface of the polishing tape 42 against theperiphery of the wafer W, and the air cylinder 45 as an actuator formoving the pressing member 44 toward the substrate holding surface 37 ofthe substrate holder 32 (i.e., toward the periphery of the wafer W). Thepressing member 44 and the air cylinder 45 are arranged at a back sideof the polishing tape 42. The pressing force (i.e., a polishing load)applied to the wafer W is regulated by controlling a pressure of a gassupplied into the air cylinder 45.

The tape-advancing mechanism 50 for advancing the polishing tape 42 in alongitudinal direction of the polishing tape 42 is mounted to thepolishing head 34. In this embodiment, the tape-advancing mechanism 50is fixed to the polishing head 34. In one embodiment, the tape-advancingmechanism 50 may be provided at a location away from the polishing head34.

The tape-advancing mechanism 50 includes a tape-advancing roller 50 a, anip roller 50 b, and a motor 50 c configured to rotate thetape-advancing roller 50 a. The motor 50 c is mounted to a side surfaceof the polishing head 34. The tape-advancing roller 50 a is secured to arotational shaft of the motor 50 c. The nip roller 50 b is adjacent tothe tape-advancing roller 50 a. The nip roller 50 b is supported by anon-illustrated mechanism, which biases the nip roller 50 b in adirection indicated by arrow NF in FIG. 5 (i.e., in a direction towardthe tape-advancing roller 50 a) so as to press the nip roller 50 bagainst the tape-advancing roller 50 a.

When the motor 50 c rotates in a direction indicated by arrow in FIG. 5,the tape-advancing roller 50 a is rotated to advance the polishing tape42 from the feeding reel 51 to the take-up reel 52 via the polishinghead 34. The nip roller 50 b is configured to be rotatable about its ownaxis. During polishing of the wafer W, the tape-advancing mechanism 50advances the polishing tape 42 in its longitudinal direction at apredetermined speed (e.g., several millimeters to several tens ofmillimeters per minute). The polishing head 34 includes the plurality ofguide rollers 43. These guide rollers 43 each guide the polishing tape42 such that the polishing tape 42 advances in a direction perpendicularto a tangential direction of the wafer W.

During polishing of the wafer W, a frictional resistance is generatedbetween the polishing tape 42 and the periphery of the rotating wafer W.Since the pressing member 44 is held by the air cylinder 45, thisfrictional resistance acts as a lateral shear force on the pressingmember 44. When the air cylinder 45 exerts a constant pressing force onthe pressing member 44, the frictional resistance between the polishingtape 42 and the periphery of the wafer W may change depending on amaterial constituting the surface of the periphery of the wafer W. Forexample, when an oxide film constituting the surface of the periphery ofthe wafer W is removed by the polishing tape 42, a silicon layer whichis an underlying layer is exposed. The exposure of the silicon layerresults in a change in the frictional resistance. Therefore, a point oftime at which the oxide film is removed can be determined from thechange in the frictional resistance.

The polishing head 34 includes a shear-force detection sensor 70 fordetecting a shear force acting on the pressing member 44 due to thefrictional resistance between the polishing tape 42 and the periphery ofthe wafer W. The shear-force detection sensor 70 is a tactile sensorwhich includes a sensor element 71 having carbon microcoils (CMC). Morespecifically, the shear-force detection sensor 70 includes the sensorelement 71 fixed to a front side of the pressing member 44, and anelectric circuit 72 electrically connected to the sensor element 71.

The polishing head 34 has a polishing-tool pressing surface 46 forsupporting the back side of the polishing tape 42 which is the polishingtool and for pressing the polishing tape 42 against the periphery of thewafer W. In this embodiment, the back side of the polishing tape 42 issupported by the sensor element 71, and the polishing tape 42 is pressedagainst the periphery of the wafer W by the sensor element 71.Therefore, the entire polishing-tool pressing surface 46 is constitutedby the sensor element 71. In one embodiment, a part of thepolishing-tool pressing surface 46 may be constituted by the sensorelement 71, and the other part may be constituted by the pressing member44. In another embodiment, the sensor element 71 may be embedded in thepressing member 44 or may be fixed to the back side of the pressingmember 44. In this case, the polishing-tool pressing surface 46 isconstituted by the pressing member 44.

FIG. 6 is a perspective view showing the shear-force detection sensor 70shown in FIG. 5. The sensor element 71 has an elastic resin block 71 a.The carbon microcoils (not shown) are located in the elastic resin block71 a. More specifically, the carbon microcoils are uniformly dispersedin the elastic resin block 71 a. In one embodiment, the elastic resinblock 71 a is constituted by a silicone block.

During polishing of the wafer W, a shear force F acts on the pressingmember 44 due to the frictional resistance between the polishing tape 42and the periphery of the rotating wafer W. A direction of the shearforce F coincides with a tangential direction of the wafer W at acontact point of the polishing tape 42 and the periphery of the wafer W,and is parallel to the substrate holding surface 37 and thepolishing-tool pressing surface 46.

An electrical characteristic of the sensor element 71, in which thecarbon microcoils are disposed, changes depending on an external forceapplied to the sensor element 71. Specifically, when the external forceis applied to the sensor element 71, an impedance of the sensor element71 changes. The electric circuit 72 applies an alternating voltage tothe sensor element 71, detects the impedance of the sensor element 71,and outputs a numerical value that directly or indirectly indicates theimpedance. This numerical value varies depending on a magnitude of theexternal force applied to the sensor element 71. Therefore, theshear-force detection sensor 70 is configured to output an index valuecomprising a numerical value that directly or indirectly indicates themagnitude of the shear force F.

During polishing of the periphery of the wafer W, the air cylinder 45applies a constant pressing force E to the pressing member 44, so thatthe pressing member 44 presses the polishing tape 42 against theperiphery of the wafer W with the constant pressing force E. At thistime, the shear force F acts on the pressing member 44 and the sensorelement 71 due to the frictional resistance between the polishing tape42 and the periphery of the wafer W. The pressing force E and the shearforce F are perpendicular to each other. The shear-force detectionsensor 70 detects a combination force of the pressing force E and theshear force F. When the frictional resistance changes as a result ofpolishing of the periphery of the wafer W, the shear force F changeswhile the pressing force E remains constant. Therefore, the index valueof the shear force F output from the shear-force detection sensor 70changes with the change in the frictional resistance.

The sensor element 71 is integral with the pressing member 44 and islocated just behind a polishing point (i.e., the contact point of thepolishing tape 42 and the periphery of the wafer W). Therefore, theshear-force detection sensor 70 can directly detect the shear force Fgenerated at the polishing point. In other words, the shear-forcedetection sensor 70 can rapidly and accurately detect a change insurface condition of the periphery of the wafer W.

As shown in FIG. 6, the electric circuit 72 of the shear-force detectionsensor 70 is electrically connected to an operation controller 80. Theindex value of the shear force F output from the shear-force detectionsensor 70 is sent in the form of a signal to the operation controller80. The operation controller 80 is configured to determine a polishingend point at which the index value reaches a threshold value. Morespecifically, the operation controller 80 includes a memory 110 storinga program for determining the polishing end point at which the indexvalue reaches the threshold value, and a processer 120 for executing theprogram. The operation controller 80 is constituted by a dedicatedcomputer or a general-purpose computer.

The operation controller 80 terminates the polishing operation based onthe polishing end point at which the index value reaches the thresholdvalue. Specifically, the operation controller 80 instructs the polishinghead 34 to stop its polishing operation, and instructs the stage motor39 of the substrate holder 32 to stop its operation. As a result,polishing of the periphery of the wafer W is terminated.

FIG. 7 is a perspective view showing another embodiment of theshear-force detection sensor 70. Structures of this embodiment, whichwill not be specifically described, are the same as those of theembodiment shown in FIG. 6, and duplicate explanations will be omitted.In this embodiment, the shear-force detection force 70 includes a loadcell 75 coupled to the back side of the pressing member 44. The electriccircuit 72 shown in FIG. 6 is not provided. The load cell 75 is locatedbetween the air cylinder 45 and the pressing member 44. The load cell 75is fixed to the back side of the pressing member 44, and is coupled tothe air cylinder 45. In this embodiment, the polishing-tool pressingsurface 46 is constituted by the pressing member 44.

The pressing force E generated by the air cylinder 45 is transmitted tothe pressing member 44 through the load cell 75. In this embodiment, theload cell 75 comprises a biaxial load cell capable of separatelydetecting the pressing force E and the shear force F perpendicular toeach other. In one embodiment, the load cell may be a uniaxial load cellcapable of detecting only the shear force F.

The load cell 75 outputs an index value that directly or indirectlyindicates the magnitude of the detected shear force F. The load cell 75is electrically connected to the operation controller 80, so that theindex value of the shear force F output from the shear-force detectionsensor 70 is sent in the form of a signal to the operation controller80. The operation controller 80 determines the polishing end point atwhich the index value reaches a threshold value.

According to this embodiment, the load cell 75 is located right behindthe polishing point (i.e., the contact point of the polishing tape 42and the periphery of the wafer W). Therefore, the load cell 75 candirectly detect the shear force F. In other words, the shear-forcedetection sensor 70 can rapidly and accurately detect the change insurface condition of the periphery of the wafer W.

The shear-force detection sensors 70 shown in FIGS. 6 and 7 are eachconfigured to output the index value of the shear force F which variesin accordance with the frictional resistance between the polishing tape42 and the periphery of the rotating wafer W. If the center of the waferW deviates from the center of the substrate holding surface 37, theindex value of the shear force F periodically fluctuates, as shown inFIG. 8. Thus, the operation controller 80 is configured to detect aperiodic change in the index value sent from the shear-force detectionsensor 70, calculate an amount of eccentricity and a direction ofeccentricity of the center of the wafer W from the center of thesubstrate holding surface 37 based on the detected periodic change, andoperate the XY moving device 38, before a next wafer is polished, tomove the substrate holding surface 37 in a direction as to eliminate theamount of eccentricity.

The amount of eccentricity can be calculated from an amplitude of theperiodic change in the index value of the shear force F sent from theshear-force detection sensor 70. The direction of eccentricity can becalculated from a rotational angle of the substrate holding surface 37corresponding to a peak of the index value that changes periodically.The rotational angle of the substrate holding surface 37 can be obtainedfrom a rotary encoder (not shown) attached to the stage motor 39.

As described above, the XY moving device 38 is configured to move thesubstrate holding surface 37 and the stage motor 39 in the X directionand the Y direction which are perpendicular to each other. The operationcontroller 80 instructs the XY moving device 38 to move the substrateholding surface 37 and the stage motor 39 in a direction in which thecalculated amount of eccentricity is eliminated. With such an operation,the next wafer is placed on the substrate holding surface 37 by atransporting device (not shown) such that the center of the next wafercoincides with the center of the substrate holding surface 37. As aresult, uniform polishing of the periphery of the wafer is achieved.

The operation controller 80 is configured to control the operations ofthe polishing apparatus including the polishing head 34 and thesubstrate holder 32. The operation controller 80 in this embodiment isconstituted by a dedicated computer or a general-purpose computer. FIG.9 is a schematic view showing a configuration of the operationcontroller 80. The operation controller 80 includes the memory 110 inwhich a program and data are stored, the processer 120, such as CPU(central processing unit), for performing arithmetic operation accordingto instructions contained in the program stored in the memory 110, aninput device 130 for inputting the data, the program, and variousinformation into the memory 110, an output device 140 for outputtingprocessing results and processed data, and a communication device 150for connecting to a network, such as the Internet.

The memory 110 includes a main memory 111 which is accessible by theprocesser 120, and an auxiliary memory 112 that stores the data and theprogram therein. The main memory 111 may be a random-access memory(RAM), and the auxiliary memory 112 is a storage device which may be ahard disk drive (HDD) or a solid-state drive (SSD).

The input device 130 includes a keyboard and a mouse, and furtherincludes a storage-medium reading device 132 for reading the data from astorage medium, and a storage-medium port 134 to which a storage mediumcan be connected. The storage medium is a non-transitory tangiblecomputer-readable storage medium. Examples of the storage medium includeoptical disk (e.g., CD-ROM, DVD-ROM) and semiconductor memory (e.g., USBflash drive, memory card). Examples of the storage-medium reading device132 include optical drive (e.g., CD drive, DVD drive) and memory reader.Examples of the storage-medium port 134 include USB port. The programand/or the data electrically stored in the storage medium is introducedinto the operation controller 80 via the input device 130, and is storedin the auxiliary memory 112 of the memory 110. The output device 140includes a display device 141 and a printer 142.

The operation controller 80 operates according to the instructionscontained in the program electrically stored in the memory 110.Specifically, the operation controller 80 determines the polishing endpoint of the wafer W at which the index value, which indicates themagnitude of the shear force detected by the shear-force detectionsensor 70, reaches the threshold value. The program is stored in anon-transitory tangible computer-readable storage medium, and theoperation controller 80 is provided with the program via the storagemedium. The operation controller 80 may be provided with the program viacommunication network, such as the Internet.

The polishing apparatus shown in FIG. 2 operates according to apolishing recipe stored in the operation controller 80. The polishingrecipe comprises operation instructions that represent operatingconditions (which are also referred to as polishing conditions) of thepolishing apparatus when polishing a periphery of a wafer. In oneexample, the polishing recipe includes specific command values of thepressing force to be generated by the air cylinder 45, the rotationalspeed of the wafer, flow rates of pure water supplied from thepure-water supply nozzles 57, 58 onto the wafer, the advancing speed ofthe polishing tape 42, etc.

In one embodiment, a computing system that can be used for setting anoptimal polishing recipe is provided. FIG. 10 is a schematic viewshowing the computing system. As shown in FIG. 10, the computing systemincludes a server 205 connected to polishing apparatuses 200, aplurality of polishing heads provided in each polishing apparatus 200,and a wafer-inspection device (substrate-inspection device) 201 by anetwork 202. The server 205 is constituted by a general-purpose computeror a dedicated computer. The server 205 may be installed in a factorywhere the polishing apparatuses 200 are disposed, or may be a so-calledcloud server connected by the network 202 such as the Internet.

Each of the polishing apparatuses 200 is a polishing apparatus includinga plurality of polishing heads 34, one of which is shown in FIG. 2.Specifically, each of the polishing apparatuses 200 is configured topress polishing tapes 42 against a periphery of a wafer by pressingmembers 44 to polish the periphery. In this embodiment, thewafer-inspection device (or substrate inspection device) 201 is aparticle counter which is configured to count the number of particlespresent on a surface of the wafer (substrate).

The wafer polished by the polishing apparatus 200 is transported to thewafer-inspection device 201 by a transporting device (not shown). Thewafer-inspection device 201 counts the number of particles on thesurface of the wafer whose periphery has been polished, and sends thenumber of particles to the server 205 via the network 202. The polishingapparatus 200 sends polishing data to the server 205 via the network202. The polishing data include the index value of the shear forceoutput from the shear-force detection sensor 70 when the polishingapparatus 200 is polishing the wafer, the above-described command values(rotational speed of the wafer, etc.) contained in the polishing recipe,and information output from each sensor, motor, etc. Each time one or apredetermined number of wafers are polished, the wafer-inspection device201 counts the number of particles on the polished wafer, and sends thenumber of particles to the server 205. Similarly, each time one or apredetermined number of wafers are polished, the polishing apparatus 200sends the polishing data including the index value of the shear forceand the command values contained in the polishing recipe to the server205.

Each time the server 205 receives the number of particles and thepolishing data, the server 205 stores learning data comprising acombination of the number of particles and the corresponding polishingdata. The server 205 perfoiins machine learning using the learning data,and constructs a model for calculating a predicted number of particlesfrom parameters including the index value of the shear force and thecommand values contained in the polishing recipe. Examples of machinelearning include neural networks and deep learning. The learning dataincreases cumulatively as polishing of a wafer is performed. Therefore,the server 205 regularly or irregularly performs the machine learningusing the learning data to update the model. A user can use theconstructed model to search for parameters that can reduce the predictednumber of particles.

In one embodiment, instead of the number of particles, the number ofchips obtained from one wafer may be included in the learning data. Inthis case, the model is a model for calculating the predicted number ofchips obtained from one wafer.

The previous description of embodiments is provided to enable a personskilled in the art to make and use the present invention. Moreover,various modifications to these embodiments will be readily apparent tothose skilled in the art, and the generic principles and specificexamples defined herein may be applied to other embodiments. Therefore,the present invention is not intended to be limited to the embodimentsdescribed herein but is to be accorded the widest scope as defined bylimitation of the claims.

What is claimed is:
 1. A polishing apparatus for polishing a peripheryof a substrate, comprising: a substrate holder having a substrateholding surface for holding the substrate, the substrate holder beingconfigured to rotate the substrate holding surface; a polishing headconfigured to press a polishing tool against the periphery of thesubstrate on the substrate holding surface; and an operation controllerconfigured to control operations of the substrate holder and thepolishing head, wherein the polishing head comprises: a pressing memberconfigured to press the polishing tool against the periphery of thesubstrate; and a shear-force detection sensor configured to detect ashear force acting on the pressing member due to a frictional resistancebetween the polishing tool and the periphery of the substrate, theshear-force detection sensor being configured to output an index valueindicating a magnitude of the shear force, and wherein the operationcontroller comprises a memory storing a program configured to determinea polishing end point at which the index value reaches a thresholdvalue, and a processer configured to execute the program.
 2. Thepolishing apparatus according to claim 1, wherein the shear-forcedetection sensor comprises a tactile sensor including a sensor elementhaving carbon microcoils, and the sensor element is fixed to thepressing member.
 3. The polishing apparatus according to claim 2,wherein the sensor element further has an elastic resin block, and thecarbon microcoils are located in the elastic resin block.
 4. Thepolishing apparatus according to claim 3, wherein: the polishing headhas a polishing-tool pressing surface configured to support a back sideof the polishing tool and to press the polishing tool against theperiphery of the substrate; and at least a part of the polishing-toolpressing surface is constituted by the sensor element.
 5. The polishingapparatus according to claim 1, wherein the shear-force detection sensorcomprises a load cell coupled to a back side of the pressing member. 6.A polishing method of polishing a periphery of a substrate, comprising:holding the substrate on a substrate holding surface; rotating thesubstrate holding surface together with the substrate; polishing theperiphery of the substrate by pressing a polishing tool with a pressingmember of a polishing head against the periphery of the substrate;during polishing of the periphery of the substrate, detecting a shearforce acting on the pressing member due to a frictional resistancebetween the polishing tool and the periphery of the substrate by ashear-force detection sensor; determining a polishing end point at whichan index value indicating a magnitude of the shear force reaches athreshold value; and terminating polishing of the periphery of thesubstrate based on the polishing end point.
 7. The polishing methodaccording to claim 6, wherein the shear-force detection sensor comprisesa tactile sensor including a sensor element having carbon microcoils,and the sensor element is fixed to the pressing member.
 8. The polishingmethod according to claim 7, wherein the sensor element further has anelastic resin block, and the carbon microcoils are located in theelastic resin block.
 9. The polishing method according to claim 8,wherein: the polishing head has a polishing-tool pressing surfaceconfigured to support a back side of the polishing tool and to press thepolishing tool against the periphery of the substrate; and at least apart of the polishing-tool pressing surface is constituted by the sensorelement.
 10. The polishing method according to claim 6, wherein theshear-force detection sensor comprises a load cell coupled to a backside of the pressing member.